In such prostheses it is generally endeavored to fit the sleeve as precisely as possible to the contours of the limb stump, in order to achieve, besides a firm seating of the prosthesis, as broad as possible a distribution of pressure upon the surface area. Recent developments have provided that the sleeve, as a result of "pumping" in the walking process there occurs a subpressure, whereby the sleeve, possibly even without additional aids, is held onto the stump. Studies have concluded that, assuming a prosthesis sleeve is well fitted in such manner, in the stump there takes place to a certain degree a hydrostatic pressure compensation. On the other hand, however, it has also been found that not all areas of the stump are equally suited for the pressure absorption, but rather, in principle, besides some zones that are more pressure-sensitive, there are other zones that are better suited to absorb external pressure. It has been ascertained that volume changes of the stump occur more noticeably in certain areas than in others. Such volume changes may occur in the short term, for example, through temperature differences and metabolically conditioned swellings or contractions depending upon, among other things, the time of day, or may occur in the longer term through weight gain or loss of the patient, muscular atrophy or the like. While attempts have been made to compensate for the differing pressure absorption capacities of the different areas of the stump by providing an attachment sleeve that is contoured, such as a design which includes an inner sleeve that fits within an outer sleeve, such a design has inherent deficiencies. Furthermore, it is difficult to attach such a conventional prosthesis for a limb which requires a narrow sleeve. For such a prosthesis, there is a relatively conventional procedure where a stocking is placed over the stump and the loose end of the stocking is drawn out through a closable opening at the end of the sleeve. Then the stocking is removed through the opening of the sleeve until finally only the stump remains in the sleeve. As should be evident, this process is difficult in the case of a narrow sleeve.
U.S. Pat. Nos. 1,893,853 and 2,634,424, and German patent DE-GM 1,810,432 disclose devices and techniques for providing an attachment sleeve that fits the changing stump contour and to provide a more comfortable prosthesis for the wearer, by including in the attachment sleeve a cushion that is inflatable with a valve. Such prior art devices, however, are directed to a uniformly inflatable cushion, even if partially subdivided, which completely surrounds and is cohesive with the stump. German patent DE-GM 1,882,630 is directed to a similar device which, in order to reduce rocking of the stump with respect to the air cushion, provides an inlay of porous plastic material inside the air cushion.
The present invention is therefore directed to providing a thigh prosthesis which readily compensates for volume changes of the stump by the exertion of pressure in the form or manner of a correction pad. In the case of thigh amputations, the stump is much shorter and the thigh bone (femur) tends assume inside the stump an unnatural, so-called abduction position (a position spread outward), whereby the muscular bias tension required for the stabilization of the pelvis is reduced on the outside of the stump.
The foregoing problem is solved by the characterizing features of the claimed invention. The claimed invention is also directed to additional advantageous features and alternative embodiments thereof.
In accordance with the invention, the particular placement of the inflatable cushions make it possible for the prosthesis to compensate for changes of the stump volume in a very compatible manner. In accordance with another aspect of the invention, there is provided a means to correct the false or misplaced position of the femur in the form of another inflatable cushion disposed in the dorsolateral zone which provides a relative adduction position (a spread position, i.e., a position appearing swung toward the plane of symmetry of the body). Further, the invention makes it possible even to introduce into the thigh prosthetics a certain degree of prepackaging, since the invention may be adapted to fit with a relatively extensive variety and shapes of individual stumps. The prior art, in GB-PS 269,606 and DE-PS 742,945, discloses a relatively extended, mechanically spring-loaded cheek inside a leg prosthesis shell which is adjustable by means of screws.
The cheek features of the invention also have special importance since they make it possible, in combination with the good surface adhesion of the sleeve to the stump to provide a unique stump end contact, a feature which is extremely desirable from an orthopedic as well as from a general medical point of view. In addition, in accordance with the invention, it is possible to prevent an excessively sensitive narrowing of the stump in the circumferential zone with compression manifestations conditioned thereby and, furthermore, to introduce a substantial part of the prosthesis supporting force in a quite natural manner over the femur into the hip joint.
The arrangement of an inflatable cushion in the stump end region beside an annular one in the circumferential zone is known in principle from EP-OS 0 151 834 which is directed to a foldable lower-leg prosthesis for occasional use, for example in shower stalls. That prosthesis, however, presents no prosthesis sleeve which is even half-way adapted to the stump form.
With respect to the features inflatable cushion of the invention claimed, it should be noted that those features are, taken only by themselves, partly disclosed in U.S. Pat. No. 3,671,980 and Austrian Patent No. 364,073 relating to the fixing of a lower-leg prosthesis by means of one or more inflatable tori over the knee of the prosthesis wearer.